The statistics for limb loss are sobering. Approximately 2 million people in the United States suffer from limb loss. Each year more than 185,000 amputations occur in the United States. It is estimated that one out of every 200 people in the U.S. has had an amputation. The statistics for limb loss in developing countries are even more troubling. Worldwide it is estimated that 650,000 people suffer from upper-extremity limb loss.
Many prosthetic limbs are currently controlled by electromyography (EMG) and are referred to as myoelectric prostheses. Electromyography monitors the electric potential of flexor and extensor muscles in the remaining portion of the limb. Using the differential between the flexor and extensor muscles potential, it can be determined whether to close or open a prosthetic hand. This system requires the user to consciously flex and relax muscles in order to control the artificial hand, because the activity of the remaining muscles would have normally controlled a different movement within the limb than the output of the prosthesis.
Other prostheses are actuated using mechanical and/or biosensors. Biosensors detect signals from the user's nervous or muscular systems, which is relayed to a controller located inside the device. Limbic and actuator feedback may be used as inputs to the function of the controller. Mechanical sensors process aspects affecting the device (e.g., limb position, applied force, load) and relay this information to the biosensor or controller, for example force meters and accelerometers. A prosthesis controller may be connected to the user's nervous and muscular systems as well as to the prosthesis itself. The controller may send intention commands from the user to the actuators of the device, and may interpret feedback from the mechanical and biosensors to the user.
Primary motor function of human muscles is directed within the motor cortex of the brain. The primary motor cortex is responsible for motion execution and the premotor cortex is responsible for motor guidance of movement and control of proximal and trunk muscles. While sections of the motor cortex are relatively well mapped to muscles and/or muscle groups, understanding brain activity within such sections of the motor cortex is not well established. Previous attempts of brain imaging have typically focused on large portions of the brain to map general zones of the brain to general functions.